A (meth)acrylic acid-based copolymer can express an excellent chelating action and an excellent dispersing action because the copolymer has many carboxyl groups or salts thereof. Accordingly, the (meth)acrylic acid-based copolymer can be used in various applications, such as a dispersant, a water treatment agent, and a scale inhibitor.
As the (meth)acrylic acid-based copolymer capable of expressing an excellent chelating action and an excellent dispersing action, there has been proposed a (meth)acrylic acid-based copolymer containing, as structural units, a structural unit derived from a sulfonic acid (salt) group-containing monomer and a structural unit derived from (meth)acrylic acid (salt) (see, for example, Patent Literatures 1 and 2).
However, such related-art (meth)acrylic acid-based copolymer containing, as structural units, a structural unit derived from a sulfonic acid (salt) group-containing monomer and a structural unit derived from (meth)acrylic acid (salt) as described above involves a problem in that the copolymer cannot express a sufficient effect on the dispersion of hydrophobic particles, though the copolymer can express an excellent effect on the dispersion of charged particles.